A hydraulic fracturing technology is a main means for improving recovery ratio of low-permeability and ultralow-permeability oil and gas fields, and a proppant is solid particles used in oil hydraulic fracturing for supporting cracks so as to prevent re-closure of the cracks. During the fracturing process, the proppant serves as a medium for supporting the cracks to provide a conduction channel for extracting oil and gas, therefore the selection of the proppant is crucial for increasing the yield of the oil and gas fields. At present, proppants widely used at home and abroad mainly comprise natural quartz sand, sintered ceramsite and resin-coated proppants.
The quartz sand generally refers to natural silica sand and is mainly applied to fracturing operation of shallow low-closure pressure wells, and the shape of the quartz sand is similar to a spherical shape, so that the quartz sand has a certain fluidity, relatively low strength and poor anti-breaking capability. The sintered ceramsite is mostly obtained by high-temperature calcination (1380-1420° C.) of bauxite, oxides of silicon and other ore, and is mainly used for a middle-deep well fracturing process, but the ceramsite proppant has the shortcomings of great energy consumption, limited resources, high cost, large density and the like. The two proppants produce a large quantity of fragments and fine mealy sand during the using process due to the need of bearing greater impact force and closure pressure, and the fragments and fine mealy sand will block the cracks and further reduce the diversion capability of the cracks. Therefore the two proppants can not meet the increasing technical requirements of the fracturing process.
The resin-coated proppant is generally prepared by coating epoxy resin, phenolic resin, furan resin or combination thereof, serving as a binding agent, on the surface of quartz sand, ceramsite or walnut shell. Resin-coated proppants with different functions can be obtained by modifying the binding agent. The selective oil-permeable and water-resistant proppant is prepared by introducing a hydrophobic group with low surface energy into the molecular chain of a resin through a chemical method, making the obtained resin film have a better hydrophobicity and further improving the water-resistant performance of the proppant, therefore obtaining a functional proppant with the oil-permeable and water-resistant performance.
CN101531893A provides a functional pre-cured resin-coated proppant, which is prepared by adding an organic silicon compound with an active group and a hydrophobic group to react with a resin during the coating and curing process of the resin. During this process, the molecules of the organic silicon compound is connected to the cross-linked network of a resin film, and the hydrophobic group of the organic silicon compound which belongs to a low-surface-energy substance is coated on the surface of the resin, so that the contact angle θ formed when the solid phase contacts a liquid phase on the surface thereof is more than 90°, forming a hydrophobic structure, therefore the surface of the resin-coated proppant has hydrophobic and oleophilic properties, which improve the separation effect of oil and gas from water and reduce the oil extraction cost; and simultaneously, the proppant has better water resistance due to good hydrophobicity of the resin film, the anti-breaking capability of the proppant is improved, and the diversion effect is better. However, the hydrophobic proppant in the prior art still has some disadvantages. Although low surface energy materials such as organic silicon compounds are added to modify the resin so as to improve the water-resistant effect of the hydrophobic proppant, but the outer surface of the resin film is smooth, and generally when low surface energy materials are used to modify the surface of a smooth solid, the maximum water contact angle is only 120°, therefore when the hydrophobic proppant is used for the fracturing process of a middle-deep well oil layer or an oil layer with high displacement pressure, the solid phase-liquid phase contact angle on the outer surface of the proppant is possibly lager than 120°, which will greatly reduce the water-resistant effect of the proppant, or even make the proppant lose the water-resistant effect, so the application working conditions of the proppant in the prior art are limited. Therefore, in order to improve the water-resistant effect of the oil-permeable and water-resistant proppant and make the oil-permeable and water-resistant proppant applicable to various working conditions of the fracturing process, the structure of the coating material needs to be improved.